1. Field of Invention
This invention relates to an innovative retrofit connector that permanently connects the roof to the outside wall to create buildings that are stronger and more resistant to hurricanes and earthquakes.
2. Description of Prior Art
Recent studies of hurricane damage on wood-frame buildings indicate that extensive damage was generated to a house by strong winds, when the roof rafters, roof trusses, and roof purlins twisted or were torn from the outside wall.
Roof sheathing ties all the rafters or purlins together on a wood frame house, and the roof sheathing ties all the roof trusses together when a masonry or wood-frame house is constructed with trusses. If the rafters or trusses rack or twist from the wind forces, the roof sheathing can detach from the roof allowing rain to enter the house.
Sheathing that is tightly secured to the rafters or trusses and subsequently fastened to the walls, helps transfer uplifting forces to the walls and henceforth to the foundation. If the roof sheathing fails, the trusses collapse, and the walls usually fall down as they can not stand by themselves against strong winds.
Failure of the outside wall sheathing is common during hurricanes, because of inadequate fastening of the sheathing to the underlying structural members. This invention helps prevent the wall sheathing from splitting, racking, and detaching from the wall. The extreme negative pressure of a hurricane blows out the sheathing from walls, but this invention holds the sheathing tight to the walls, as sheet metal joints perform better than nailed joints in high winds and during seismic activity.
Studies of damage after Hurricane Andrew show several problems with the attachment of roof rafters and roof trusses that this invention solves.
Roof overhangs act like wings, creating huge uplifting forces during strong winds. This uplift tears apart the rafters that are toe-nailed to the header or top plate. The uplift can also twist rafters and roof trusses weakening the toenailed connections and causing detachment.
The one thing that ties together the top plate, studs, and sill plate is the outside sheathing. This invention effectively ties together the rafter, top plate, and outside sheathing to form a continuous load-path to the sill plate. Attaching my invention to the rafter and top plate junction puts the nails perpendicular to the uplifting force and would require shearing the nails in order to lift the rafter or truss.
One significant factor in building construction is precision framing, where the rafter is installed directly above the stud. Unfortunately, in existing houses this is rarely the case.
Post-and-beam construction is very common in older homes in mild-weather areas, and we have found that the wall studs, or in this case, posts, are only under every fourth rafter, and the rafters can be 4-feet on center. Usually, the posts are directly under where the top plate butts up against the top plate in the run. The rafter is to one side of this butt joint, so the rafter does not line up directly over the post.
On newer stud-wall construction, we have seen that studs rarely line up directly under the rafters. We saw a house where the walls have studs 16-inches on center, constructed with a roof that had rafters 24-inches on center. This means the only rafter and stud that will line up to form a continuous load-path is every fourth stud or every other rafter. What are the odds that they will exactly line up?
Another problem with home construction is on mis-installation of prior art hurricane clips that are made for new construction and covered by wall sheathing. After Hurricane Andrew, there were many examples of careless and inferior attachment of hurricane clips or they were entirely missing. One company has visited new construction sites and documented many examples of shoddy and incorrect application of their products.
To achieve a continuous load-path on existing houses the outside sheathing must be taken into account. The most important tie in an existing house is between the rafter and top plate or roof truss and top plate. Any uplifting wind force on the roof must be transferred to the walls. In tropical climates, the roof purlin, an intermediate structural member, may separate from the rafter with the roof sheathing.
My invention effectively ties together the rafter or roof truss, top plate, and outside sheathing (and indirectly, the wall studs) to form the most practical and economical continuous load path from the roof to the foundation.
During an earthquake, the floor, wall, and roof diaphragms undergo shearing and bending. The shear forces from the roof boundary members are transferred to the top of the shear wall by way of toenails to the top plate. To withstand and transfer the shear loads, the connection between the roof and wall must be strong.
The outside sheathing provides lateral stability to the walls, preventing racking. The sheathing also absorbs and transfers earthquake forces by becoming a shear wall.
An earthquake can send motion into a house and separate the sheathing from the walls. The sheathing can come loose from the walls by the nails popping out or the plywood splitting away from the nails driven on it""s edge. Some codes allow sheathing to be stapled to the wall studs, which is a weak connection. This invention helps prevent the sheathing from pulling away from the wall during earth movements.
Steel connectors, between different components of a wood-frame buildings superstructure, provide continuity so that the building will move as a unit in response to seismic activity (Yanev, 1974).
A number of connectors have been developed to tie together the structural members of a house under construction. Up until this invention, nobody had seen how to make a connector that could tie sheathing to the underlying structural members and connect to the side or xe2x80x9cmeatxe2x80x9d of a rafter or roof truss without having material hanging down.
My co-pending application, Ser. No. 08/191,852, is a retrofit hurricane clip. Although it can be mounted on 2xc3x97 rafters, it was designed for large timber rafters such as 4xc3x97 stock, and has a web member that can be seen from the side. This invention uses a saddle and side webs for lateral support, and can not be seen from the side, hence it is stealth-like.
The leading manufacturer of wood construction connectors, the Simpson Strong-tie Company, shows no retrofit hurricane connectors in their catalog.
There are a number of ties that fasten the rafter to the top plate while a house is being constructed including: Knoth U.S. Pat. No. 5,561,949, McDonald U.S. Pat. No. 5,560,156, Colonias U.S. Pat. No. 5,380,115, Stuart U.S. Pat. No. 5,335,469, Colonias et al U.S. Pat. No. 5,109,646, Commins U.S. Pat. No. 4,714,372, Gilb U.S. Pat. No. 4,572,695, and Gilb et al U.S. Pat. No. 4,410,294.
These are good inventions, but they are difficult to retrofit onto existing houses without demolition of existing parts on a house. None were designed or patented to be retrofit on to an existing house.
The prior art hurricane clips provide little lateral strength, even when using a left and right. The prior art cannot tie the outside sheathing to the underlying top plate and roof rafter. They cannot clear frieze boards and prevent the outside sheathing from being sucked off during the extreme negative pressure of a hurricane.
The prior art inventions do not prevent the outside sheathing from splintering and disconnecting during earth tremors. They do not have multiple uses such as tieing the floor joists to the wall studs, the weakest parts of a wood-frame house in an earthquake.
Frye""s anchor system, U.S. Pat. No. 5,311,708, is patented as a retrofit, but it does not tie the rafter to the top plate, cannot clear frieze boards, and ties into the weakest thin edge of the rafter while splitting it with bolts. Frye""s 708 also provides no lateral support against side movements.
Netek""s reinforcing tie, U.S. Pat. No. 5,257,483, is patented as a retrofit and may clear frieze boards, but it is temporary, and like Frye, ties into an even weaker thin edge of the end of the rafter. Netek""s 483 also provides no lateral support against side movements.
There are several retrofit apparatus for securing roofs using cables. Adams U.S. Pat. No. 5,570,545 and Winger U.S. Pat. No. 5,319,896 are both temporary, meaning a homeowner must be home to deploy and anchor the ephemeral cables. The anchors can only be as secure as the nearby soil and the cables do not prevent the walls from bowing or blowing out.
There are a number of joist hangers that fasten to a joist and vertical member while a house is being constructed including: Colonias et al U.S. Pat. No. 5,104,252 and Gilb U.S. Pat. No. 4,480,941. These are good inventions, but they provide little lateral strength, and they are difficult to retrofit onto existing houses.
Joist hangers have a small ledge that supports all the weight from the joist beam. They hang the weight from the edge, rather than supporting the weight on top of the edge. They are also thin and parallel to the long dimension of the joist beam, concentrating all that carrying weight onto a vertical thin-section of the vertical member.
Gilb""s complicated hanger, U.S. Pat. No. 4,261,155, is strong, but cannot be retrofit on to a house.
Prior art connectors relied on angled nailing, to provide lateral support, which is complex to, manufacture, and very difficult to install on a completed house.
Accordingly, several objects and advantages of my invention are that it helps secure the roof and wall of a building to make the building a solid unit and preventing it from being destroyed by hurricanes and earthquakes.
This invention helps prevent the roof from being blown off the walls of an existing building. It keeps the roof rafters and roof trusses tightly secured to the outside sheathing and underlying top plate of the wall.
This invention helps prevent the roof rafters and roof trusses from twisting during strong winds, thereby preventing detaching of the roof material and underlying roof sheathing. It stiffens the edge of the roof and the top of the wall, helping to transfer lateral loads to the whole roof and walls.
This invention helps prevent the wall sheathing of a building from detaching from the wall studs during an earthquake. It helps make the outside wall into a stable shearwall, transferring shear forces into the foundation and ground.
One object of this invention is to make each outside wall on a house into a shearwall, that is, able to transfer forces without breaking or disconnecting. By tying the outside sheathing securely to the top plate and rafter or roof truss, the plywood can reliably transfer and dissipate shear, lateral, and uplift forces to the ground.
During an earthquake or a hurricane, a building with my invention will be a sturdy unit, resisting and transferring destructive forces to the ground.
Many older homes were constructed with the best materials and competent carpenters, but used the time-honored method of connecting the rafter to the top plate with nails driven into the edge of the rafter. This weak connection, called toe-nailing, is still in use today. Even if prior art hurricane clips were used in construction, the homeowner can""t tell and those clips don""t hold the outside wall sheathing to the wall.
Outside sheathing is usually secured to a wall stud under a rafter. Builders line up each plywood sheet on a wall stud for nailing. This invention has a large base member that keeps the plywood from separating from the wall during a hurricane. It also prevents the plywood sheets from sliding past each other during an earthquake.
Mounted on the roof rafter or roof truss, my invention resists uplift, the most destructive force during a hurricane. Mounted on the top plate and wall sheathing, my invention prevents the wall sheathing from being blown off or sucked out by the extreme negative pressure of a hurricane.
During an earthquake, when my clips are mounted on the roof and walls, they will make each member into a shear wall. The secured plywood will absorb and dissipate earth movements, without becoming detached from the underlying structural members. It will also prevent the sheathing from sliding past each other.
This would improve the house beyond existing building codes, as sheet metal joints have been proven to perform better than nailed joints during hurricanes and earthquakes.
Another object of this invention is the large surface area. This area prevents the plywood sheathing from splitting during hurricanes or earthquakes. The large surface area provides more strength in the connecting or hold-down process.
Yet another advantage of this invention is during earthquakes, nails can sometimes bend with the movements of the house, but screws often break. Even though screws hold tighter than nails and provide a tight connection against uplifting forces from hurricanes, they are less resistant against earth movements. This invention absorbs and transmits most of the forces during an earthquake and hurricane so nails and/or screws can be used as fasteners.
Another advantage is that since the invention absorbs and transfers earthquake and hurricane forces, less nails and nailing could be used. Also, screws could be used in the invention in earthquake areas with less fear that the heads will shear off
Still another advantage of the invention is in the ability to prevent plywood sheets from sliding past or over each other during an earthquake. Previously, only nails had to shear, but this entire connector must be sheared for the invention to fail.
Still another advantage is that with the roof rafters and roof trusses better able to resist twisting, roof sheathing will stay firmly attached and roofing material will now have a better chance of staying on during strong winds and earth movements. In addition, with the sheathing now firmly connected, new materials may be attached to the roof, such as solar electric panels, without fear of them being blown off.
In areas with brush or forest fire danger, fire-proof material or heavy material, such as tile, stone or metal, can now be applied to the roof with less danger of being blown or shaken off during earth tremors or high winds. Fire-proof materials such as stucco or brick veneer can be applied to the wall sheathing with less chance of being shaken off during earth movements.
Earth tremors and hurricanes always destroy the weakest parts of a house. By making each envelope of a house, the vertical walls and roof envelope into a strong unit, there will be less damage.
It is a further object of this invention that it easily, quickly, and economically protects houses from the destructive forces of earthquakes and hurricanes. It is a still further object that the connectors and fasteners are strong, attractive, permanent, functional, uncomplicated, simple to manufacture, easy to install, and economical. All of the embodiments can be made from a single sheet metal blank, without any welding.
A further object is that this invention can be used on various size sheathing, rafters, roof trusses, studs, wood or metal I-beams, TJI, and glue-lams, all made from wood or metal. There may be insurance discounts for homeowners who have this invention installed on their houses.
As a retrofit, a handy homeowner can install this invention, or have it installed. The homeowner can easily see that the home is protected instead of wondering if hurricane clips were installed correctly during construction, or installed at all.
Traditional toe-nailing of the rafter is at the bird""s-mouth, a notch cut into the rafter where it rests on the top plate. By cutting out material from the rafter, a bird""s-mouth weakens the rafter. Toe-nailing only two nails from either side grasps only a small edge of the rafter, and the nail only extends into the top 2xc3x97 of the top plate.
Tests were done by the Colorado School of Mines on my co-pending retrofit hurricane clip, application Ser. No. 08/191,852. The tests showed that the rafter split lengthwise, due to uplifting force, before my 852xe2x80x2 clip failed.
This new retrofit invention strengthens the rafter to top plate connection by vastly increasing the spacing and amount of nails in the thickest part or xe2x80x9cmeatxe2x80x9d of the rafter. This clip also strengthens the bird""s mouth by wrapping on either side of the rafter and keeping it from splitting along the long measure.
As a retrofit, an insurance agent can observe that the home is protected and give appropriate discounts. Perspective home buyers can perceive that the building is protected, so the seller has a good selling point and can ask for a better price.
Since the stealth clip is a retrofit, and is not covered by sheathing or gypsum board, the invention is much thicker than prior hurricane clips and tensile values are dramatically increased.
Another advantage is with the top webs angled away from vertical, they form an upside-down flying buttress. This tremendously increases resistance to outward thrusts. This makes the roof much stronger and able to resist more weight such as thick snow, ice, or volcanic ash, and heavy roofing material such as tile, insulated roofing, solar collectors, and satellite dishes.
This invention takes the place of a left and right prior art hurricane clip, thus cost and installation time is substantially reduced. Installation can be accomplished with a power nailer or powered screw gun.
The left and right tabs, and the saddle combine to cradle the rafter, significantly increasing lateral strength over prior hurricane clips. The saddle carries no weight of the rafter, the bird""s mouth cut of the rafter distributing the weight onto the top plate. Hence the saddle can have a curved shape, angled shape, compound angles, flat seat, or rounded seat.
Since this invention cradles the rafter or roof truss on the bottom, and left and right side, and has wide tabs anchored to the outside wall, torsional twisting is significantly reduced over prior art hurricane clips, as is cross-grain splitting.
Since the left and right tabs, and the saddle combine to significantly increase lateral stiffness, no part of the invention hangs below the rafter, hence it is invisible from the side. Architects and homeowners approve that this hurricane clip is concealed.
The left and right tabs, that are installed on opposite sides of the rafter have offset nail holes. Nails driven into the rafter will be offset from each other lessening wood splitting and vastly increasing holding power.
This invention does not require any removal of frieze boards or wood trim from the house. On houses where a frieze board is installed between rafters or roof trusses, this invention has an offset between the top and base webs that allows the invention to be installed as a retrofit. The offset clears any frieze board, wires, or trim that sticks out from the wall.
If the frieze board is warped or is slanted away from the house, the angled top web""s position will clear it. If the frieze board is angled on one side of the rafter and straight on the other side of the rafter, this invention will still not be hindered in being retrofit on to a house.
By adding a simple embodiment, the roofing material and roof sheathing can be held down to the roof rafter. This invention can hold down roof sheathing to the rafter or roof truss, providing great rigidity to the entire house. This makes the house, significantly more resistant to strong winds and earth tremors.
In tropical climates, where hurricanes are common, roof purlins are used to support the roof sheathing, usually corrugated metal roofing, which is too thin to fit between the rafters. This invention can hold down a roof purlin and corrugated metal roofing using a simple embodiment.
Edges of the clip are slightly rounded for strength, ease of handling, and avoiding stress fracturing associated with sharp corners.
These and other objectives of the invention are achieved by simple and economical connectors that allow a builder or home owner to quickly and easily secure the weakest parts of a building against earth tremors and high winds.
Advantages of each will be discussed in the description. Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description.